The present invention relates to a method of regulating the position of a clutch actuator, specifically in a motor vehicle equipped with an automated shift transmission and an electronic clutch management system.
The term xe2x80x9cshift transmissionxe2x80x9d in the present context is used primarily for a transmission with different gear ratios that are shifted manually by the driver of the vehicle by means of a shift lever. Shift transmissions of a variety of configurations are known in the prior art. A common trait of shift transmissions is that the gear shift process has two phases: a) moving the shift lever in a selector track to one of a plurality of shift tracks of the transmission, and b) moving the shift lever within the selected shift track to engage the intended gear ratio.
In addition to the manual shift transmissions just described, the state of the art also includes automated shift transmissions, in which the phases of selecting the shift plane and engaging the intended gear ratio are performed by actuators that are coupled by means of a force transfer mechanism to internal shifter elements of the transmission such as a central shift-control shaft and shift-control rods.
The known automated shift transmissions of the foregoing description are used in combination with an electronic clutch management system which automatically engages and disengages the clutch, so that all the driver has to do is select the intended gear. The clutch is operated by the electronic clutch management system.
In the course of recent technical efforts to optimize the shift process in an automated shift transmission, the requirements have substantially increased for the clutch actuator to move into and hold a given actuator position precisely. However, with the requirement for increased precision in a position-seeking control loop in an actuator driven by an electric motor, the latter has to work for longer time intervals, which increases electric power consumption. When regulating the clutch to a given target position, the electric motor performs only very small movements, so that a disproportionate amount of the power supplied to the electric motor is converted into heat.
A position-seeking controller turns off when the targeted actuator position has been set within a given hysteresis bandwidth where the deviation from the control target is less than a given regulation threshold in the order of 0.1 to 0.2 mm. A steady bias current to the actuator is active only at times when the position controller is turned off.
A so-called hunting or after-regulation behavior of the position control loop occurs if the actuator does not have an adequate amount of holding force or holding torque, so that the counteracting force can push the actuator outside the aforementioned hysteresis bandwidth of the regulated position. This can occur only at a time when the position controller is turned off. As the hysteresis bandwidth is exceeded, the position controller is reactivated to regulate the actuator back to the target position. The back-and-forth movement where the actuator is pushed out of and then regulated back into the target position is referred to herein as after-regulation or hunting.
The present invention therefore has the objective of providing a method of regulating the position of a clutch actuator, specifically in a motor vehicle equipped with an automated shift transmission and an electronic clutch management system, so that the power consumption of the clutch actuator is minimized while the full functionality of the electronic clutch management system is maintained.
To meet the foregoing objective, the invention proposes a method of regulating the position of a clutch actuator in a vehicle that is equipped with a clutch control device, for example of the kind known as electronic clutch management system. The method can be described in three steps, as follows:
a) The clutch control device determines the current operating state of the vehicle based on a plurality of operating parameters of the vehicle.
b) The clutch control device selects a set of regulation parameters out of a plurality of available regulation parameter sets.
c) The clutch control device regulates the position of the clutch actuator through a position-control loop, using the selected set of regulation parameters.
This method has the advantage that the regulation parameters are adapted to different operating states of the vehicle, so that the regulation process depends on the situation. The adaptation of the parameters is such that the regulation process is made more efficient, resulting in reduced energy consumption.
In road tests of the method, it was found that the regulation could be performed at a reduced level of precision more than 50% of the time without a loss in driving comfort.
In a preferred embodiment of the invention, at least two predetermined sets of regulation parameters are available, from which the clutch control device selects a specific parameter set dependent on the operating state of the vehicle. With the different parameter sets, the regulation can be better adapted to different situations.
Instead of transmitting the entire set of regulation parameters, a binary flag is used to transmit the operating status from the clutch control device to the position-regulating control loop and to thereby communicate which of the regulation parameter sets is to be selected. If there are more than two sets of parameters, an appropriate number of flags has to be used for the data transmission. The object is to minimize the volume of data communication between the clutch control device and the position-regulating control loop.
A set of regulation parameters preferably includes the servo loop constants known, respectively, as the P-, I- and D-coefficient for the proportional, integrating, and differentiating term of the control function, a precision criterion, as well as the limits of the hysteresis band, i.e., the points where the position controller is switched off and back on.
The precision requirement can be divided into a fine and coarse precision criterion, to work with two precision ranges in the most elementary application of the inventive concept. It is also possible to use a higher number of ranges.
If two ranges are used, the switch-off threshold under the fine-precision criterion is preferably around 0.02 mm from the target position and the threshold for switching the controller back on is preferably around 0.1 mm from the target position. Under the coarse-precision criterion, the preferred switch-off threshold is around 0.1 mm from the target position and the preferred threshold for switching the controller back on is around 0.2 mm from the target position.
The clutch actuator has an electric motor, whose speed and direction are controlled in order to actuate the clutch. An electric motor has numerous advantages over a hydraulic system. Importantly, the problems of leakage and of aggressive hydraulic fluids are avoided with an electric motor.
In a preferred embodiment, a position sensor is integrated in the clutch actuator to determine the current actuator-travel position in absolute terms.
After the actuator has been set and regulated to a prescribed target position and the position controller has been switched off, it is possible that the position-holding force or holding torque of the clutch actuator is not strong enough to keep a lever of the clutch mechanism in a set position, particularly if the clutch requires a strong clutch-release force. Thus, the lever is pushed back by the force of the clutch, so that a position control loop has to regulate the actuator back to the target position. This increases the load on the clutch actuator, and the after-regulation can also manifest itself through a chattering of the clutch.
To prevent after-regulation, it is necessary to oppose the clutch force with a counteracting force. This counteracting force is generated by applying a steady bias current to the clutch actuator during the time phases when the position controller is switched off. Given that the clutch-release force of the clutches varies from one vehicle to the next within a very wide tolerance range, the level of the bias current has to be selected individually in each vehicle.
In a further embodiment of the method according to the present invention, the regulation of a clutch actuator to a a targeted position can be described by the following steps:
a) The clutch control device determines the actual position of the clutch actuator.
b) The clutch control device compares the actual position to a target position of the clutch actuator.
c) The clutch control device determines the extent and the direction of an after-regulation occurring in the clutch actuator.
d) The clutch control device updates the level of the bias current to the clutch actuator in accordance with the extent and direction of the after-regulation detected under step c).
This has the advantage that the optimized level of the bias current in the clutch actuator reduces the overall amount of energy used during after-regulation periods of the clutch actuator. By adjusting the level of the bias current, the need for an after-regulation is in many cases avoided.
The bias current to the clutch actuator is turned on only during time periods when the position-regulating loop is switched off.
According to a preferred embodiment of the invention, the amount of the bias current is dependent on the position of the clutch actuator. The bias current as a function of the clutch position follows a characteristic or profile that can be expressed as a percentage of the maximum possible actuator current.
Preferably, the profile of the bias current is stored as a default profile before a vehicle is put into service. The default profile indicates the amount of current to be applied to the clutch actuator at given points of its displacement range that are spaced at predetermined intervals.
It is advantageous and also adequate to use, for example, four reference points for the profile of the bias current. If the reactive force opposing the actuator is known qualitatively as a function of actuator displacement, one could use a higher density of reference points in a portion of the range where the reactive force is strong and a lower density where the reactive force is comparatively weak. If evenly spaced reference points are used, the distance between them could be about 0.5 mm.
Based on the amount of after-regulation, the respective values of the current profile are adjusted for all reference points.
The adjustment is preferably made in predetermined percentage increments of the voltage or current, or it can be based on the amount of after-regulation, or in can occur in variable steps.
However, the value of the bias current at each reference point is limited by a maximum permissible value and/or by a maximum permissible difference between the values at adjacent reference points.
There are numerous possibilities for determining the current profile during an operating phase of the vehicle, of which the following are preferred:
a) A new calculation, starting from initial values of zero, is made at every start-up of the vehicle when the ignition is switched on.
b) A new calculation, starting from a profile of default values, is made at every start-up.
c) A new calculation, starting from a profile of most currently stored values, is made at every start-up.
d) A new calculation is made as in case c), but the values at individual reference points are given different weights.
e) A new calculation is made at every start-up, using any combination of the foregoing possibilities a) through d).
A further embodiment of the inventive method can be described by the following sequence of steps:
a) The clutch control device determines actual position values of the clutch actuator.
b) The clutch control device determines targeted position values of the clutch actuator.
c) The clutch control device determines whether the current regulating process is an initial move or an after-regulation to the current target position, based on comparing actual and targeted position values.
d) The clutch control device generates a bias current to the clutch actuator in accordance with the results of steps a) to c).
Dependent on the comparison in step c) of the foregoing method, the amount and the polarity of the bias current to the clutch actuator can be adapted and optimized so that, as a result, the method will save energy.
To perform the foregoing method, the clutch actuator preferably has an integrated position sensor to detect the actual position value Kactual.
The values Ktarget for the target position determined in step b) of the method are assigned to one of three groups corresponding to three different conditions of the actuator. The groups are defined according to the trend in successively detected values, i.e., whether the values increase, decrease, or stay constant from one to the next. An increasing trend is taken as an indicator that the actuator is pushing the clutch farther than the targeted displacement position; a decreasing trend is taken as an indicator that the clutch actuator is receding from the targeted displacement position; and a constant value indicates an intermediate condition.
The values Ktarget are assigned to the group of increasing values if they change monotonically in a positive direction.
More specifically, the values Ktarget are assigned to the group of increasing values if preferably at least the three most recent values of Ktarget show an increasing tendency and/or exceed a threshold value of increase from one to the next.
If the increase of three consecutive values of Ktarget exceeds a predetermined threshold, the clutch control device determines that the clutch actuator is not in a state of after-regulation.
Analogously, the values Ktarget are assigned to the group of decreasing values if they change monotonically in a negative direction.
More specifically, the values Ktarget are assigned to the group of decreasing values if preferably at least the three most recent values of Ktarget show a decreasing tendency and/or exceed a threshold value of decrease from one to the next.
If the decrease of three consecutive values of Ktarget exceeds a predetermined threshold, the clutch control device determines that the clutch actuator is not in a state of after-regulation.
The values Ktarget are assigned to the group of constant values if they do not change significantly from one to the next.
More specifically, the values Ktarget are assigned to the group of constant values if they lie within a certain bandwidth which is defined preferably as the hysteresis width that serves as a criterion for switching off the position control loop.